In automatic transmissions, a transmission oil pump is needed to provide pressure and lubrication media for the supply of hydraulically actuated frictional shifting elements and for the lubrication of gearteeth and bearing points of the transmission.
JP 2006-064009 A describes a transmission oil pump that is arranged axially parallel to the torque converter of a vehicle, which is driven by a chain drive, wherein the chain drive pinion is driven by the converter neck and is mounted by means of a slide bearing in the converter bell. In this case the chain drive pinion is statically sealed by a sealing ring against the outer diameter of the converter neck and dynamically sealed by a rectangular ring against the impeller shaft.
DE 10 2006 035 133 A1 by the present applicant describes a pump drive mechanism of a transmission oil pump of an automatic transmission, which is arranged axially parallel to the torque converter, wherein the transmission oil pump is driven by a chain sprocket wheel, itself driven by a pump impeller of the torque converter. In this case the pump impeller of the torque converter is connected to a converter hub which, starting from the pump impeller, extends in a direction away from the drive motor, being mounted radially by a radial bearing in or on a wall of the automatic transmission fixed on the transmission housing and, on the side of the radial bearing that faces away from the sprocket teeth, having a driving profile which engages with interlock in a corresponding driving profile of the converter turbine.
In the known pump drive mechanism, it is provided that, between the radial bearing and the driving profile of the converter hub when viewed axially, a radial sealing O-ring is positioned between the converter hub and the converter neck, and the converter neck itself is mounted on the transmission housing by means of a radial bearing and rotationally sealed relative to the housing.
From the prior art, it is also known to drive a transmission oil pump of an automatic transmission, the pump being arranged axially offset relative to the torque converter, by means of a chain drive arranged behind a centering plate in which the torque converter is also mounted, such that the driven sprocket wheel of the chain drive is mounted on the converter neck which is made as a through-shaft and is functionally connected to the converter neck by means of an axially displaceable driving profile.
In this case the mounting of the driven sprocket wheel is made axially displaceable and is in the form of a narrow clearance fit. In this way the sprocket wheel is advantageously axially decoupled from the torque converter, so that the chain of the chain drive can be guided without drift. Moreover, thanks to the narrow clearance fit, the internal pressure of the converter can be sealed in with low leakage losses and the leakage can be used in a selective manner for wetting the converter neck seal on the outside, for lubricating the converter neck mounting and for lubricating the chain drive.
Disadvantageously, however, when a vehicle is stationary and particularly after a longer period at rest, the toroidal inside space of the converter can partially drain through the gap seal of the sprocket wheel, i.e. through the narrow clearance, and when the motor is restarted this results in delayed starting-off of the vehicle since the torque converter first has to be filled.
In the prior art the lubrication pressure limiting valve of the transmission lubrication oil supply as a whole is integrated in the hydraulic transmission control unit.